Gas water heaters have not extensively used electronic controls because of associated problems with electronic ignition systems and availability of an electrical outlet in close proximity to the water heater. There are two common types of electronic ignition: hot surface and direct spark ignition. Hot surface igniters are expensive, easily broken and require a considerable amount of electrical energy to operate. In comparison, spark igniters are inexpensive, durable and use little energy, however, the transient electrical pulses or voltage spikes from known spark ignition systems may undesirably interfere with electronic circuits. Due to these shortcomings, many gas water heaters use a non-electronic standing pilot ignition system.
As the Department of Energy (DOE) increases energy efficiency (EF) ratings for water heaters, manufacturers will need to look beyond foam insulation techniques to meet the new increased EF standards. Incorporating electronic controls and ignition systems can raise the energy efficiency ratings by eliminating the standing pilot and reducing the negative effects of stacking on energy efficiency. Stacking occurs when frequent small draws of water create different temperatures throughout the tank resulting in increased peak temperatures at the top of the tank.
Unlike electric water heaters, gas water heaters only have one source of heat and one temperature sensor. The source of heat is a burner typically located underneath the tank. A temperature sensing device near the bottom of the tank controls when the burner is turned on or “cuts-in”. A typical gas water heater has a cold water inlet with a dip tube. As hot water is drawn from the tank, cold water passes through the dip tube and enters near the bottom of the tank and temperature sensor. As the cold water mixes with the water at the bottom of the tank, the temperature sensing device will initiate a cut-in. Frequent short draws will initiate multiple cut-ins causing the water at the top of the tank to become much hotter (stacking) than the set point temperature of the temperature sensing device at the bottom of the tank. Thus, there is a need to improve the performance of current water heaters to prevent stacking and thereby improve the Energy Efficiency (EF) rating.
Another shortcoming of current gas hot water heaters equipped with single temperature sensor control systems is a symptom referred to by some water heater manufacturers as “morning sickness”. Morning sickness refers to a condition in which there has been an extended period of time in which no hot water has been drawn from the tank. The hot water at the top of the tank mixes with the colder water at the bottom of the tank until it reaches a consistent temperature throughout the tank. To prevent stacking, on single temperature sensor control systems, the control will not turn on the burner until the water temperature at the temperature sensor located near the bottom of the tank is 30° F. below the set point temperature. If the water heater is set at 120° F., the control will not turn on the burner until the temperature sensor reaches 90° F. If the water heater has been sitting without a draw for an extended period of time, the water temperature is as low as 95° F. throughout the whole tank when there is a need for hot water resulting in no hot water available or a considerably diminished capacity of hot water available when needed. In light of this shortcoming, a need exists to improve the performance of a water heater to assure that there is hot water available when needed.
Yet another obstacle in using an intelligent electronic control in gas water heaters is the availability of electricity in close proximity to the water heater. Most gas waters heaters sold are replacement units that are placed in homes where there is no electrical outlet nearby. Therefore an additional need exists for the electronic control to operate in a “cordless” mode for extended periods of time.
Fuel-connected appliances may comprise a spark ignition system to ignite fuel at a burner. In known single electrode spark ignition systems for appliances, fuel emanates from a burner that is typically grounded to the chassis of the appliance. The chassis, however, may not be properly grounded. For example, the chassis of an appliance is resting on nonconductive plastic or rubber wheels, or the chassis is resting on a nonconductive surface such as wood. In order to ignite the fuel, a voltage potential difference is generated between an electrode and the burner. The voltage potential difference is in the range of 12,000 to 20,000 volts. Consequently, a 12,000 to 20,000 volt ignition spark is generated between the electrode and the burner. An ignition spark of this magnitude may cause transient electrical pulses or voltage spikes to undesirably interfere with the performance of electronic circuitry of the appliance. For instance, the transient electrical pulses or voltage spikes may interfere with the performance of a microprocessor-based or microcontroller-based control circuit of an appliance. The transient electrical pulses or voltage spikes may also reset a microprocessor power supply that typically operates at 5 volts. In addition, the transient electrical pulses or voltage spikes may damage components of electric circuitry, may cause a microprocessor or microcontroller to incorrectly process information, and/or may cause electronic circuitry to lockup or crash.
Due to the shortcomings of known single electrode spark ignition systems when used in conjunction with electronic circuitry, manufacturers of appliances have instead used dual electrode spark ignition systems, hot surface igniters to ignite fuel, and single electrode spark ignition systems with a discrete spark module control isolated from the main microprocessor-based electronic control system. U.S. Pat. Nos. 5,003,960 and 5,033,449 disclose embodiments of a dual electrode spark ignition system. In a dual electrode spark ignition system, a spark is caused to jump from one electrode to another electrode, rather than from one electrode to chassis ground.
In order to prevent transient electrical pulses or voltage spikes from interfering with electronic circuitry, both electrodes of a dual electrode spark ignition system are heavily isolated from chassis ground and the electronic circuitry. For example, U.S. Pat. Nos. 5,003,960 and 5,033,449 utilize a ceramic insulating material to isolate the electrodes. Nevertheless, water or other conductive materials may gather on the insulating materials and short the electrodes to chassis ground and/or the electronic circuit. In addition, cracks may develop in the insulating material. As a result, water or other conductive materials may enter the cracks and short the electrodes to chassis ground and/or the electronic circuitry.
Also, in order to prevent transient electrical pulses or voltage spikes from interfering with electronic circuitry, appliance controls like those produced by Invensys of Carol Stream, Ill. and supplied to companies like Whirlpool of Benton Harbor, Mich. utilize a separate spark module control board isolated from the microprocessor control board. Besides being more costly and adding an additional component part to the appliance, the risk remains that transient electrical pulses or voltage spikes may reach the control through the cable assembly or other means.
On the other hand, a hot surface igniter may not interfere with the functions of a microprocessor or other electronic circuitry. For example, many appliance controls have significant shortcomings for use in water heaters. First, the igniter elements is made of silicon carbide or other similar fragile materials that may easily break or be damaged during shipment. Second, hot surface igniters may have a high field failure rate due to the igniter's elements burning out. Third, hot surface igniters may cost approximately seven times more than a single electrode spark igniter. Fourth, condensation shortens the life span of a hot surface igniter. Finally, hot surface igniters require a significant amount of electrical current to operate.
In light of the shortcomings of the above-mentioned systems, a need exists for a reliable and less expensive single electrode spark ignition system that does not damage or interfere with the performance of electronic circuitry and consumes very little power.